Surgical operating table with hydraulic actuating means



June 4, 1957 E. F. FULLWOOD ET AL 2,794,694

SURGICAL OPERATING TABLE WITH HYDRAULIC ACTUATING MEANS Filed Jan. 24, 1952 12 Sheets-Sheet l INVENTOR EDWARD F. FULLWOOD BY JOHN PHILIPP ATTO RN EY June 4', 1957 E. F- FULLWOOD EITAL Filed Jan. 24, 1952 12 Sheets-Shee't 2 INVENTQR EDWARD F. FULLWOOD BY JOHN PHILIPPI ATTORNEY J1me 1957 E. F. FULLWOOD EFAL 2,794,694

12 Sheets-Sheet s 20o INVENTOR" EDWARD F. vFULLWOOD 5 JOHN F'Hll' ZOI FIG. 5

-|ATTORNEY June 1957 E. F. FULLWOOD ETAL 2,794,694

SURGICAL OPERATING TABLE WITH HYDRAULIC ACTUATING MEANS l2 Sheets-$119M; 4

Filed Jain. 24, 1952 FIG. 5

INVENTQR wars BY 1 5 m ATTORNEY SURGICAL OPERATING TABLE WITH HYDRAULIC ACTUATING MEANS Filed Jan.

12 Sheets-Sheet 5 FIG. 9

E. F. FULLWOOD EIAL June 4, 1957 INVENTOR EDWARD F. FUILLWOOD JOHN PH LIPP BY i I t III!" ATTORNEY FIG. \0

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June 1957 v E. F. FULLWOOD ElAL 2,794,694

SURGICAL OPERATING TABLE WITH HYDRAULIC ACTUATING MEANS Filed Jan. 24, 1952 12 Sheets-Sheet 6 771T I 7 4/ K13 210' 209 l6. 4 4 El o ll 1 j 2 e", W 6/ I l3 13' I6 j/ 1 208 203 2o3 4 k INVENTOR EDWARD E FULLWOOD Y Pl FIG: \5 H. #131 ATTORNEY June 4, 1957 EQ F. FULLWOOD Er'AL 2,794,694

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June 4, 1957 E. F. FULLWOOD ETAL 2,794,694

SURGICAL OPERATING TABLE WITH HYDRAULIC ACTUATING MEANS Filed Jan. 24, 1952 12 Sheets-Sheet a 23 I67 A' c B' 167 7I I L R l O I: I I I I69 L I68 I94 I 7 I93 I77 4 1; I89 I74 T I73 I75 I) I I I48 I I92 I67 f I85 I86 -l67 234 I I46 I65 I64 f 1 a I \67 I72 INVENTQR I75 EDWARD F FULLWOOD I73 BY JOHN PHILIPP I74 FIG. \9 [I I;

ATTO R N EY SURGICAL OPERATING TABLE WITH HYDRAULIC ACTUATING MEANS Filed Jan. 24, 1952 June 4, 1957 E. F- FULLWOOD EIAL.

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June 4, 1957 E. F. FULLWOOD ETAL 12 Shets-Sheet 11 FIG. 25

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E. F. FULLWOOD ETAL 12 Sheets-Sheet 12 FIG. 29

INVENTOR EDWARD F FULLWOOD BY JOHN PHILIPEI ATTORNEY FIG.3\

United States Patent SURGICAL OPERATING TABLE WITH HY- DRAULIC ACTUATING WANS Edward F. Fullwood and John Philippi, Madison, Wis, assignors to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application January 24, 1952, Serial No. 268,162

Claims. (Cl. 311-7) This invention relates to surgical operating tables.

Due to the highly specialized nature of present surgical practices, the operating table has become increasingly important as a tool of the surgeon, who relies upon the complex adjustments of the table to position the patient in a manner providing the most desirable access to the field of the operation. It is frequently necessary, in the course of an operation, to rearrange the table structure in order to alter the position of the patient. Present surgical techniques require operating tables that are capable of extensive and varied adjustments and which are equipped with readily-accessible control mechanism for making the necessary adjustments quickly, without delaying the operation. Since the utmost care must be exercised in moving the patient gently, so as to avoid shock, injur or discomfort, the table mechanism must also be capable of precisely-controllable movements.

In order to provide operating tables particularly adapted to meet the exacting standards of present surgical practices, it has been proposed to utilize motor-driven adjusting mechanisms. For example, one suggestion has been to provide operating tables with electric motor devices operatively associated with the adjustable portions of the table structure. The adjustment of the table would thus be facilitated and controllable from a remote station by selective operation of the separate motor devices. It is objectionable, however, in most cases to use electric devices in operating rooms, where an explosion hazard exists due to the presence of anesthetic gases. Usually only the most essential electrical equipment is located in the area of operation and then only when stringent specifications are met by the provision of suitable explosion-proof apparatus. While a type of explosion-proof electric motor is available, the motor housing of this motor is not compact and the necessity of providing the necessary number of motors of this type, or even of the ordinary type, for completely controlling all the movements of the table creates a cumbersome and impractical structure.

Some tables have utilized hydraulic means for actuation of the table adjusting mechanism. This type of operating table overcomes the explosion hazard, but there has yet been no hydraulic table which has proved completely acceptable for surgical purposes and commercially satisfactory. One of the difiieulties has been that certain mechanical limitations have had to be incorporated in the table construction in order to accommodate the hydraulic or fluid actuating devices. Thus all of the variations of adjustment and the ranges of movement of the table members which are desired could not be obtained. Furthermore, tables designed or intended for complete hydraulic actuation have heretofore had inadequate fluid control circuits and valve means. To compensate for these deficiencies, some hydraulic tables have been only partially mechanized by the hydraulic devices and have had the remaining adjustments made by manual means. In prior hydraulic tables, controlled rates of movement of the table members in both directions of movement has not been accomplished. There has also been the inherent "ice problem of avoiding leakage of oil, or other actuating fluid, from the control circuit.

It is an object of this invention to provide an improved hydraulic operating table which overcomes the inherent disadvantages in previous tables of this type.

Another object of the invention is to provide an improved fluid control circuit for operating tables having selective and compound table movements.

Another object is to provide an improved table structure especially adapted to accommodate fluid actuating mechanisms for the entire table without limiting the ranges of adjustment thereof and which alfords a strong, rigid support for the patient in all positions.

A further object of the invention is to provide an improved arrangement of valve means and valve adjusting mechanism for controlling the movements of an adjustable surgical table. I

A further object of the invention is to provide discharge valve means for regulating, under predetermined conditions, the discharge flow of the actuating fluid in the control circuit of an hydraulic surgical table, to prevent excessive rates of movement of the hydraulic cylinder table actuating means.

A further object is to provide improved speed control means operable in connection with the table control circuit for adjusting the rates of movement of the cylinder devices.

A still further object of the invention is to provide improvements in fluid circuits for series-connected surgical table actuating cylinders.

Other objects and advantages of the invention will be better understood by referring to the following description and drawings of a preferred embodiment of the invention in which: i

Fig. l is a side elevation, partially in section, of an operating table arranged and constructed in accordance with the invention;

Fig. 2 is a top plan view, partially in section, of the table shown in Fig. 1;

Fig. 3 is a vertical sectional elevation taken substantially along line 33 in Fig. 1, partially sectioned in the pedestal looking in the direction of the arrows;

Fig. 4 is a sectional elevation taken along line 4-4 in Fig. 2 looking in the direction of the arrows;

Fig. 5 is a sectional elevation taken along line 55 in Fig. 2 looking in the direction of the arrows, the table platform sections having been removed therefrom and the reversed-Trendelenburg position of the table being shown in dotted lines;

Fig. 6 is a sectional elevation taken substantially along line 66 in Fig. 5 looking in the direction of the arrows, including also a side-tilted position of the table frame in dotted lines;

Fig. 7 is a sectional elevation taken along line 77 in Fig. 6 looking in the direction of the arrows, showing the table frame and associated cylinder mechanism in the tilted position indicated in dotted lines in Fig. 6;

Fig. 8 is a sectional elevation taken substantially along line 8-8 in Fig. 7 looking in the direction of the arrows, certain parts being omitted to simplify the drawing;

Fig. 9 is a sectional elevation taken substantially along line 99 in Fig. 4 looking in the direction of the arrows;

Fig. 10 is a plan view sectioned along the line 10-10 in Fig. 9 looking in the direction of the arrows;

Fig. 11 is a sectional elevation taken along the line 1111 in Fig. 9 looking in the direction of the arrows, showing the detailed construction of a compound cylinder device mounted in the table frame for supporting portions of the back and seat table sections and the kidney bridge;

Fig. 12 is a sectional plan view taken substantially on 3. line 1212 in Fig. 1 looking in the direction of the arrows;

Fig. 13 is a sectional elevation taken substantially on line 1313 in Fig. 12 looking in the direction of the arrows;

Fig. 14 is a front partial view, partly in section, taken substantially along line 1414 in Fig flpillustrating. the master control valve mechanism and showing the compactly-arranged valve units; I Fig. 15 is a sectional elevation taken on line in Fig. 14;

Fig. 16 is a sectional elevation taken on line 16--16 in Fig. 14, the valve units being omitted;

Fig. 17 is an end view of the dial face at the end of the arm casing in Fig. 14; p

'Fig. 18 is a sectional plan view of the master control valve assembly including the valve units, taken substantially along the line 1818 in Fig. 16;

Fig. 19 is an enlarged partial section taken transversely through the valve assembly in Fig. 18 illustrating the structure of the valve units therein;

Fig. 20 is a diagrammatic illustration of the distribution system of the fluid circuit for the operating table including the hydraulic cylinder devices and selector valve housing of the master control valve mechanism;

Fig. 21 is a diagrammatic illustration of the supply system of the fluid circuit for the operating table including the fluid pump and reversing valve housing of the master control valve mechanism;

Fig. 22 is a diagrammatic illustration of an alternative form of the fluid circuit embodying speed control means;

Fig. 23 is a sectional view taken substantially along the line 2323 in Fig. 18 looking in the direction of the arrows;

Fig. 24 is a partial sectional plan view of a modified formof the master. valve assembly in Fig. 14 taken substantially along the line 18-18 in this figure, showing the inclusion of a speed control valve unit;

Fig. 25 is an enlarged sectional view'taken' transversely through the valve units in Fig. 24 showing the cam operating means;

Fig. 26 is a longitudinal sectional view of the variablepressure relief valve shown schematically in the circuit diagram of Fig. 21;

Fig. 27 is a longitudinal sectional view of the bypass regulating valve of the speed control mechanism shown schematically in the circuit diagram of Fig. 22;

Figs. 2831 are schematic illustrations showing the table in some of the various operating positions obtainable by adjustment of the control mechanism which are respectively, 'Trendelenburg position, center break or Mayo-kidney position, reflex-abdominal position, and the chair position.

The preferred embodiment of the invention, as shown in the drawings, generally described, comprises an hydraulic operating table (Figs. 1 and 2) having a plurality of adjustable members, hydraulic. cylinder devices operatively associated with each of the adjustable members, and a fluid system including master control valve means for selectively administering fluid to the cylinder devices. The table structure includes a base, a platform structure, and a pedestal adapted to raise or lower the platform. The table platform structure comprises a platform consisting of a plurality of table sections and a rigid supporting frame in which the table sections are adjustably mounted, each table section having a fluid-actuated motor device for adjusting the table sections relative to each other and with respect'to the table frame. Preferably, the frame carries the'back, seat, and leg sections and a kidney bridge which is movable vertically with respect to the mounting frame.

Universal means are provided (Fig. 4-8) for mounting the table frame on the pedestal whereby the table platform may be tilted as a unit laterally'and longitudinally,

2,794,694 V a V .4 such adjusting means having an extensive angular range of displacement and being so constructed as to aflord exceptional structural rigidity throughout its entire range of motion. The universal means comprises a bracket pivotally mounted on the table pedestal in which first and second double-acting fluid cylinder devices are mounted in relative transverse planes.

The system for administering fluid to the cylinder devices (Figs. 20 and 21) is an improved fluid circuit which includes a reservoir, a pump for supplying fluid underrelatively high pressure to the circuit from the reservoir, low pressure conduit means for returning fluid to said reservoir, selector valve units for selectively completing operating circuits through the respective hydraulic cylinders, and reversing valve means having reversible high and low fluid pressure connections with the selector units to produce a reversible flow of actuating fluid in said operating circuits. The reversing valve means thereby controls the direction of movement of the associated table members. The circuit also contains a variable pressure-relief valve for limiting the rate of discharge from the circuit when the cylinder devices are moved in the direction of the force which is exerted by the load sup ported thereon. A modification of the control circuit (Fig. 22) includes an adjustable speed control valve and a circuit bypass conduit wherein speed adjustments are made through manipulation of the control valve. The speeds of operation are maintained independent of the load carried by the table through the eflect of a regulating valve in the by-pass conduit. In addition, over-travel means are incorporated in some of the cylinder devices to permit flushing of the circuit and coordination between cylinder devices that are series-connected for simultaneous operation. 7

The selector valve units are mounted in a common selector valve body (Figs. 14 and 18). Each of the valve units is operated to open a circuit to a corresponding cylinder mechanism or mechanisms by valve actuation means mounted in the selector valve body. Adjusting means therefor extend outwardly to a point within each reach of the operator at all times and there is provided indexing means associated therewith, whereby the fluid circuit actuated in each of the respective positions of the selector adjusting means is indicated. The reversing valve means are preferably mounted on the same housing as the selector valve means forming a master valve assembly housing. The adjusting means for the reversing valve extend substantially co-extensively with the adjusting means for said selector valve so that both of these valve means may be operatedfrom a single position.

Referring now in detail to the specific construction shown in the drawings, an operating table constructed and arranged in accordance with the preferred form of the invention as shown in Fig. 1, there being omitted, however, from this and the other figures illustrating the table structure, the'several fluid conduits making up the fluid control circuit which connects the several fluid-actuated elements and valves of the table circuit. Confusion of the structural drawings due to such detail is thereby avoided, while the necessary fluid circuit connections may be clearly understood by reference to the circuit diagram of Figs. 20 and 21, taken in connection with the description hereinafter. 1

The operating table is supported by a base 10 having four corner stanchions 11. Each of the stanchions contains a caster wheel 12 which is extendable by means of an hydraulic caster cylinder device 13. When the pistons in cylinder devices 13 are extended, the table is raised from the stanchion supports and rests on the caster wheels 12, facilitating movement of the table. The hydraulic caster cylinder devices are actuated by means of a foot pump 14, seen in Fig. 13 provided with an operating lever 15, the outer end of which is adapted to be depressed to actuate the pump. Fluid from the foot pump is forced into the respective cylinders 13 through series-connected conduits 16, best seen in Fig. 12, into which the cylinders 13 are tapped. To lower the table and permit the base to rest on the stanchion supports 11, a lever 17 is depressed which opens check valve means in the foot pump and permits the fluid to drain from the cylinders 13.

The base 10 comprises a housing 18 having a removable cover 19, Fig. 1, through which access may be had to the table mechanism contained therein. The base 10 houses a container, or reservoir, 20 having a vent 21 holding a supply of hydraulic fluid at atmospheric pressure for the table control circuit, an electric motor 22 and an hydraulic constant-displacement pump 23 coup-led to the motor 22. A power line 22' is connected to a source of electric current to operate motor 22 which is fully explosion proof in the manner acceptable to surgical operating room specifications. Other equipment housed therein will be described in greater detail hereinafter.

The housing 18 has a heavy, rigid base plate 24, Fig. 13, from which a central column 25 extends upwardly through the cover 19. As seen in Fig. l, the column 25 constitutes the lower section of the table pedestal 26 wherein a telescoping inner column 27 is received. The inner column 27 carries grooved guide members 28 at its lower end which ride on vertical longitudinal ribs 29 mounted in the bore of the base column 25 to prevent rotation of the telescoping column therein. Two annular bearing blocks 30, secured in the base column, receive the inner column, taking up the slack between the inner and outer columns and adding greater rigidity to the pedestal support. At the upper end of telescoping member 27 an end plate, or cap, 31 is provided on which the table platform structure designated generally at 32 is mounted through a yoke structure 33.

The table platform structure 32 may be vertically adjusted as a unit by means of the hydraulic cylinder mechanism including an upright shaft or rod 34 and piston 35, which are stanchioned in the base, and a cylinder barrel 36 which is mounted within the pedestal member 27 and depends from the end cap 31. Fluid for controlling the operation of the pedestal cylinder mechanism is admitted to the cylinder barrel above or below the piston depending upon the movement desired, while the fluid on the opposite side of the piston is permitted to exhaust from the barrel. Referring to Fig. 3, a fluid line 37 communicates with the cylinder barrel 36 through a passage 38 in end cap 31 and a connecting tube 39 which opens into the barrel chamber below the piston. A conduit 40 is received by a suitable fluid fitting in end cap 31, wherefrom a passage 41 opens through end plate 31 into the. bore of the cylinder barrel above the piston. Elevation of the table is effected by admitting high pressure fluid to the cylinder barrel above the piston through conduit 40 and passage 41 which urges the cylinder barrel upwardly and extends the pedestal. Fluid is simultaneously exhausted from the cylinder barrel through connecting tube 39, passage 38 and conduit 37. The lowering movement is accomplished by reversing the fluid circuit connections and admitting the high pressure fluid to the underside of the piston through conduit 37. Fluid in the cylinder barrel above the piston is exhausted therefrom as the pedestal is retracted. The exhausting of fluid at reduced pressure from the cylinder barrel is regulated to control the rate of displacement of the cylinder mechanism and therefore the movement of the table as will be hereinafter more fully described. The administration of the actuating fluid is controlled by valve control means in the hydraulic circuit as will also be later described.

The table platform structure 32 comprises a plurality of adjustable sections supported in a rigid frame 42, Figs. 1 and 2, including cross-beam members 43 and side members 44. The table sections include a back section 45, an intermediate section 46, a kidney bridge 47, a seat section 48 and a leg section 49. Along both sides of the table platform there are provided slide bars 50 on which slidable mounting fixtures 51 are situated. The mounting fixtures are provided for supporting the various auxiliary equipment used in conjunction with the operating table, such as a canopy frame, arm or leg slings, etc. A head rest 52 is pivotally supported on a cross member 53 having slide boxes 54 thereon that are received on extensions of the slide bars 50. The head rest is angularly adjustable about the cross member 53 and is provided with a ratchet type locking mechanism 55 to secure it in its adjusted positions. The seat section supports at its outer end clamp devices G which accommodate knee crutch supports or other equipment. The clamps G are an improved type of clamp which are particularly adapted for mounting the knee crutch support and are identical to the clamping means described and claimed in copending application Serial No. 169,268, E. F. Fullwood, which is assigned to the assignee of the present application.

Side plates 56 are fastened by bolts 56 to the side frame members 44. Thus the plates 56 constitute the side walls of a shield partially enclosing the table superstructure in the frame 42.

Back section 45 is hinged at 57, Fig. 4, to the intermediate platform section 46 and is supported on the table frame 42 for pivotal movement by hydraulic cylinder devices 58 and 59. The cylinder devices, both of which are seen in Fig. 2, are rotatably mounted on trunnion axles 60 in bifurcated portions 61 of the table flame. Each of the cylinder devices has a plunger or piston rod 62 which carries a lug 63, Fig. 4, that is hingedly received at 64 in the back section. The plungers are reciprocally movable within cylinder members 65 which are in turn piston-rod elements adapted to be reciprocated in the outer barrel portions 66 and 67 respectively of the cylinder devices 58 and 59. Thus, these cylinder devices (also shown schematically at 58 and 59 in Fig. 20) are of the compound cylinder type having inner and outer cylinders and pistonrod elements cooperating to provide a maximum displacement which is particularly useful for rotating the back section 42 through a wide range of angular adjustments. As will later be seen, the inner and outer cylinder devices may be operated independently or in unison through the table control circuit.

Fluid is delivered to and from the barrel portions 66 and 67 through fluid lines 68 and 69, and lines 70 and 71 respectively, whereby the piston rods 65 are actuated. Fluid for actuation of the inner piston rods 62 is provided by means of fluid conduits 72 and 73 in the cylinder device 58 and fluid conduits 74 and 75 in the cylinder device 59. The fluid fittings receiving the pairs of conduits 72, 73 and 74, 75 are mounted at the lower ends of the inner cylinder barrels 65 instead of opposite ends of the cylinder barrels as in conventional cylinders. In each cylinder the fittings for conduits 72 and 74 open directly into the lower ends of the respective piston chambers. The fittings receiving conduits 72 and 74 connect internally of the cylinder barrels with tubes (not shown) that pass through suitable openings in the piston members into the upper ends of the piston chamber. Thus connections for alternatively delivering fluid at either side of the piston in each of the devices are aflorded. The specific construction of the cylinders is unrelated to the present invention and has not therefore been illustrated in detail in the drawings. When the devices 58 and 59 are actuated to raise the back section, high pressure fluid is admitted through the lines 69 and 71 to the outer barrel portions 66 and 67 which causes the cylinder-piston members 65 to be drawn upwardly therein. Ejection of the inner piston rods 62 from the members 65 occurs by administering actuating fluid through the conduits 73 and 75 respectively. In order to lower the back section, the high pressure fluid is admitted to the opposite ends of the cylinders through conduits 68 and 70 in outer barrels 65 and 66 and member 92;

in lines 72 and 74 in piston-cylinder members 65, respectively; The means by which control fluid is administered to the supply conduits Will be hereinafter described.

Seat section 48 is also hinged into intermediate section id as shown at 76, Figs. 2 and 4. This section is'adjusted by hydraulic cylinders 77 and 78 which are pivoted on trunnions 79 in bifurcations 80 of frame 42. Each cylinder contains a piston rod or plunger 81 having a lug 32 which is received by pin connection 83 in the seat section.

The cylinders 77 and 78 are provided, respectively, with conduits 84 and 85 at the blank ends of the cylinders and conduits S6 and 87 at'the rod ends thereof. Fluid is administere'd'to the cylinders through these conduits to raise or lower the seat section about its hinge connection 76. For'exarnple, the seat section is elevated by admitting high pressure fluid to the blank ends of the cylinders through fluid conduits 84 and 85 which causes the piston rods 31 to be projected from the cylinders. In order to reverse the movement of the seat section, high pressure fluid is admitted to the rod-end of the cylinders through the fluid conduits S6 and 87 respectively.

Intermediate section 46 is mounted in table'frame 42 for vertical movement, which is accomplished by cylinder devices 83 and 89, Fig. 9. Enlarged portions 90 in the frame receive the cylinders wherein the barrels 91 are soldered or otherwise rigidly fixed. Each cylinder has a plunger 92 movable vertically within the cylinder barrels. Brackets 93, extending longitudinally of the table, as shown in Fig. support the section 46 on the plungers 92. The cylinder devices 88 and 89 are provided With fluid conduits 94 and '95 respectively, seen also in Fig. 3, at the upper ends of the cylinder barrels 91 and with conduits 95 and 97, respectively, at the lower ends thereof. Conduits 94. and 95 are'received on the usual fluid fittings which are mounted'in the enlarged portions 90 of the frame throughwhich passages register with openings in the side walls of the cylinders as illustrated by the opening 94 in hydraulic cylinder 88.

The vertically adjustable intermediate section 46 on which are hinged back section 45 and seat section 48 affords an improved structural arrangement of the table platform. For example, 'the inner hinge points 57 and 76, seen in Fig. 4, respectively, may be elevated simultaneously, thus producing a Mayo-kidney positioning of 1 the table platform in a single movement. In this position of the table the back and seat sections are inclined downwardly "on opposite sides of their common hinge points, so that the abdominal region of the patient is elevated. To raise section 46, high pressure fluid is admitted to the lower ends of the cylinders through the conduits 96 and 97 which urges the plungers 92 upwardly in the cylinders. To retract'the plungers 92 the actuating fluid is introduced into the upper ends of the cylinder barrels through the fluid lines 94 and 95. The control of the cylinder devices is eliected by control mechanism associated with the table hydraulic circuit which will be described hereinafter.

The kidney bridge 47 is supported on stems 98 which proiect out'of the plungers 92 of the cylinder devices 88 and S9 and are received in sockets 99 in the kidney bridge. These stems constitute inner piston rod members which are movable within the plunger members 92, as illustrated schematically in Fig. 20. The detailed construction of each of the hydraulic cylinder devices 88 and 89 which support the section 46 is shown in Fig. 11. The stem 98, it will be seen, comprises a piston rod having a piston 100 which is slidable within the bore of cylindrical piston rod The piston rod 92 carries a piston 92 whi h is receivedin the chamber 91' whereby the piston rod may be elevated to raise the intermediate section 46, as before described. The inner piston rod 98 may be operated independently of the piston rod 92 by separately controlling the actuating fluid delivered to the bore of the cylindrical rriember'92for actuation of piston 100, and .the fluid delivered to' chamber 91 for actuation of piston 92'. Piston is provided with a valve mechanism'comprising ball elements 101 which are disposed'in passage 101', through which fluid is enabled to pass between the blank-end face and the rod-end face of the piston. The ball elements are urged against openings at opposite ends of the passage 101' by a spring element 101" interposed between the ball elements. This valve construction is similar to the piston overtravel valve construction described and claimed in a co-pending application-Serial No. 233,758, E. F. Fullwood and J. Philippi, 1 led June 27, 1951, which is assigned to the assignee of the present invention. The present construction differs in that the valve is adapted to be operated only at the blank end of the cylinder to permit fluid passage through the piston, instead of both ends of the cylinder, as in the disclosure of the co-pending application. Thus in the cyliuders 92 the pistons 160 are provided with overtravel means in the downward movement of the piston. Fluid lines communicating with the blank ends of hollow piston rods 92 in the cylinders 83 and 89 respectively are indicated at 102 and 193, Fig. 9. Rod-end fluid connections for the cylinder devices are shown at 104 and 105.

When it is desired to raise the kidney bridge, high pressure fluid is supplied through conduits 102 and 193 to the blank ends of the piston rod cylinder members 92. This causes the kidney bridge to be elevated, as indicated by the dotted lines in Fig. 11, independently of the section 46 which is immobilized as long as actuating fluid is not administered to the outer cylinder barrels 91. The lower kidney bridge 47, the high pressure fluid is admitted to the cylinders 92 through the rod-end conduits 104 and 105. When the cylinder members 92 are actuated, as before described, the inner piston rods 98 and the kidney bridge are carried in the same relative position therewith. The kidney bridge is controlled by means of control mechanism associated with the hydraulic table circuit, as will be described hereinafter.

The leg section 49 is hinged by means of binge con nections 196 to the outer end of the seat section, as best seen in Figs. 1 and 2. The leg section is adjusted angularly about the hin e connections by a pair of hydraulic cylinders 107 pivoted on brackets 19% on the seat section and on lugs ll fi' on the outer end of the leg section. The cylinders 107 have cylinder barrels 107 and piston rods 10?" which form an expansible linkage adapted to rotate the hinged leg section 49. Conduits 109 are provided at the blank-cnds of the cylinders 107 and conduits 110 are provided at the rod-ends thereof. Each of these cylinder devices 107 is identical to the cylinder device shown in Fig. 2 of the above-mentioned co-pending application, Serial .No. 233,758 of E. F. Fullwood and J. Philippi; they each include the overtravel valve means operable at both ends of the piston strokes, as shown in said Fullwood et al application.

High pressure fluid is admitted to the rod-ends of cylinders 197 through the conduits 110 in order to lower the leg section. By reversing the circuit connections, the high pressure fluid is delivered to the blank-ends of the cylinders through the conduits 109 to raise the leg section. The delivery of the actuation fluid and control of the leg section cylinders is accomplished by control mechanism associated with the hydraulic circuit for the table, as will be described hereinafter. The functioning of the piston overtravel means in the control circuit will also be later described.

The table platform and frame 42, whereon the'platform sections are adjustably supported, are mounted on the table pedestal for universal movement as a unit by means of the yoke structure 33. Referring to Fig. 9, the yoke structure comprises an inverted yoke 1H having depending side members112 which are pivoted for rotation longitudinally of the table on studs 112' held in arms 113 extending downwardly from the pedestal cap.31. The yoke 111 is so formed as to include bosses 114, seen also in Fig. 4, which provide bearings in which a cylinder barrel 115 of hydraulic cylinder device 116 is journalled. The ends of the barrel 115 are fixed in flanges 117 formed in the central portions of cross-beams 43, whereby the table frame may be tilted laterally about the longitudinal axis of the cylinder 115 which acts as a hinge pin. Referring now also to Figs. 5, 6, '1', and 8, such lateral tilting movement of the frame is efiected by means of an hydraulic cylinder device 118 disposed in a plane substantially transverse to the plane of cylinder device 116 and supported on a fixed plunger, or piston rod, 119 mounted between rearward extensions 120 of yoke side arms 112 mounted centrally on the piston rod 119, and within cylinder barrel 121 is a fixed piston 121'. Barrel 121 of the cylinder device carries lugs 122 (Fig. 8) into which studs 123 are threaded and adjusted to provide a socket for engagement of ball member 124. The ball member comprises an outer universal joint connection for stirrupshaped link 125 which is hinged at 126 in flange 117 of the rear cross-beam member 43 of the table frame. The stirrup link member is pivotable vertically about the axis of hinge connection 126, but is laterally rigid with respect to the cross-beam member 43. Thus the table frame 42 is tilted by lateral movement of the barrel 121 which pulls the link 125 toward either side of its center position causing the cross-beam member 43 to be rotated about the axis of the cylinder 116. The displacement of the tilting mechanism in tilting the table frame toward the right, as viewed from the foot end of the table, is illustrated in Figs. 7 and 8 and by the dotted lines in Fig. 6. During such movement it is necessary to accommodate the relative displacement between the hinge connection 126 on cross-beam 43 which moves arcuately, and the socket connection on cylinder barrel 121 which would ordinarily be displaced on a straight line parallel to the axis of the cylinder. In this construction the barrel is permitted to rotate a small amount on the piston rod 119, as indicated by the angular displacement of the cylinder barrel from its normal position, shown in dotted lines in Fig. 7, which together with the pivotal movement of link 125 and the freedom of the ball socket joint provides a flexible driving connection. The cylinder is provided with fluid conduits 127 and 128 communicating with the bore of the cylinder barrel on opposite sides of the piston 121', as seen in Fig. 6. When the table frame is to be tilted in the direction shown by the displaced phantom figure in Fig. 6, the high pressure fluid is administered to the cylinder through conduit 127, whereupon the barrel 121 is urged to the left of this figure. Figs. 7 and 8 illustrate the displaced position of the cylinder device 118. To tilt the table in the opposite direction the high pressure fluid is administered through conduit 128.

The table platform 32 is tilted in the longitudinal plane to provide the Trendelenburg and Reverse- Trendelenburg positions by the hydraulic cylinder device 116, which is otherwise referred to as the Trendelenburg cylinder. The cylinder 116 is provided with a piston rod 129, Fig. 4, having a piston 139 which is received in the bore of the cylinder barrel 115. At its outermost end rod 129 is secured to the central portion of a crosspiece 131, which has its opposite ends fastened to rack bars 132, seen in Figs. 1 and 2. The rack bars 132 extend rearwardly in parallel relation to the piston rod 129 and are slidably received in longitudinal grooves 133 in yoke member 111, as seen in Fig. 3. The undersides of rack bars 132 are provided with teeth 134, Fig. 5, which mesh with teeth 135 formed on circular gear segments 136. The gear segments are mounted on the pedestal cap 31 by bolts 137 shown passing upwardly through the cap 31 into the lower portions of the gear segments in Figs. 4, 9, and 10. Piston 134) is thus connected with cap 31 through piston rod 129, cross-piece 131, rack bars 132 and gear segments 136; whereas the cylinder barrel 115 is fixed against axial movement in the yoke .111 by collars 117 secured to opposite ends of the barrel. Thus 10 when fluid is admitted under pressure to the cylinder 116 to cause relative displacement between the piston and cylinder barrel the yoke is moved relative to the cap and pedestal, and this motion will be an angular motion about the axis of the yoke pivots 112'. Gear segments 136 are so located that their pitch circles are in concentric relation to the circular path generated by the angular movement of the yoke 111. Thus, the rack bars 132, which are supported from the yoke by piston rod 123 and yoke grooves 133, remain tangent to the gear segments as the yoke pivots about axis 112, and the rack teeth 134 are maintained in engagement with the gear teeth 135 in all angular positions of the yoke. As the yoke 111 and frame assembly 42 mounted thereon are rotated, the rack bars rotate with the yoke and frame and move about the gear segments 136 in the manner of rocker elements; successive teeth thereon engaging with the corresponding gear teeth of the gear segments, thus maintaining a positive engagement in all positions. During such rotational movement the yoke 111 slides relative to the rack bars in the grooves 133. A displaced position of the table frame 42 is shown in Fig. 5, corresponding to a Reverse-Trendelenburg position wherein the head end of the table is elevated.

The Trendelenburg cylinder is provided with a fluid conduit 138 at the blank end and with a conduit 139 at the rod end. Fluid introduced through conduit 138 expands the chamber volume between the piston and the blank end of the cylinder causing the yoke 111 and frame 42 to be moved toward the right in this figure about the pivots 112', as indicated by the dotted lines in Fig. 5. To reverse the movement of the table or to move the table platform to a Trendelenburg position, the high pressure fluid is admitted to cylinder 115 through the rod-end conduit 139. This urges the cylinder barrel 115 fluther toward the left in Fig. 5, producing a turning movement of the yoke and table frame in the same direction.

The particular construction described for the Trendelenburg movement has the notable advantage of providing a positive engagement through the rack bars and gear segments in all angular. positions, and of providing important structural rigidity even at extreme Trendelenburg positions. Moreover, this construction permits the entire table platform to be angularly adjusted in the longitudinal plane as a unit, without necessitating any alteration of a previous relative disposition of the table platform sections. Similarly, the construction affords desirable rigidity for lateral tilting of the table platform.

The control valve mechanism for controlling the circulation of actuating fluid in the table circuit to the hydraulic cylinder devices comprises a master valve unit 140, Fig. 2, which is mounted in the frame 42 on arm extensions 141 of the side frame members 44. Fluid lines connect the master valve unit with the several cylinder devices, as will be described hereinafter. The master valve unit has operating means comprising a shaft 142 which extends outwardly toward one side of the table. The shaft 142 is received in a housing having an angle extension 143 mounted on the side plate 56 attached to frame 42 and extending upwardly and toward the head end of the table in which the controls for the valve operating means are located. The arm extension 143 terminates in a truncated dial face 144 which is at an oblique angle designed for easy vision of the dial markings by the operator. A pointer 145 is correlated with the respective positions of the valve operating means which are indicated on the dial face.

Referring to Fig. 14, the master valve unit and valve operating mechanism (described and claimed per se in the co-pending application of E. F. Fullwood, assigned to the assignee of the present application, Air Reduction Patent Project No. 216) are shown in greater detail. The valve unit 140 is a composite structure made up of a selector valve assembly 146 and a reversing valve assembly 147. The shaft assembly 142 comprises an inner shaft 148 and an outer shaft 149 wherein the inner shaft is .co-axially and rotatably disposed; the co-axial shafts being adapted to be operated independently of one another. The shaft 149 is journalled in the selector valve 146 and in an extension bearing 149 which projects from side plate 56 of the table frame and supports the shaft assembly at its outer extremity. The shaft 149 carries on its outer end a sprocket 150 which is connected by a drive chain 151 with a second sprocket 152 keyed in a shaft 153 having a hand-adjusting knob 154. Manipulation of knob 154 rotates the shaft 149 through the chain and sprocket drive whereby the selector valve mechanism is actuated, as will be described. A pair of bevel gears 155 and 156 are arranged to transmit the adjustments of the drive shaft 153 to pointer indicator 145 whereby the corresponding positions of the valve-adjusting shaft 149 will be designated on dial face 144.

Operating shaft 148 extends through selector valve housing 146 within the tubular shaft 149 and into the reversing valve housing 147. At its opposite end the inner shaft extends beyond the shaft 149 whereon is held a sprocket 157. This sprocket is linked by a chain 158 to an upper sprocket 159 which is situated on a bushing 169 adapted to revolve independently of the shaft 153 on which it is supported. A lever 161, only a small portion of which is seen in this figure, projects from the bushing member outwardly through the underside of the casing as seen in Fig. 1. The lever is adapted to be pivoted upwardly or. downwardly from its normal position shown in this figure, as indicated by the dotted line positions at 161. Such movement of the lever 161 causes rotation of the shaft 148 which actuates the reversing valve mechanism, as will be described.

The selector valve housing-146 consists of a composite structure including end plate portions 162 and 162' and a central valve block member 163. The end plates are held against the valve block by bolts, only the ends 163i of which are visible inthe drawings. Banks of valves A, B, and C are arranged circumferentially in the valve block 163 in which each valve is an independent valve unit, substantially as shown'in Figs. 18 and 19. Each valve, such as the valve B which is enlarged and sectioned in Fig. 19, is a removable unit and is of an improved construction particularly adapted for reversible fluid flow. The valve units per se are identical to the valve construction shown in 'the copending application, Serial No. 214,127, E. F. Fullwood, which is assigned to the assignee of the present application, now Patent No.'2,692,114. Each of the valves is provided with a valve seat 164, a valve stem 16S and fluid ports 166 and 167 between which the passage of fluid is controlled by the cooperation of the valve seat and the valve stem. Each of the'valves is normally closed, except when the end 172 of the valve stem 165 which protrudes into a central core chamber 173 of the valve housing is depressed by the selector valve actuating mechanism, which includes a roller cam element at 174. Referring to Fig. 18, cam element 174 comprises an elongated pin which is mounted at its opposite ends in disc plates 175 which are carried on the tubular adjusting shaft 149. The pin is disposed longitudinally within the chamber 173 and at a radius which enables it to come into contact with the protruding valve elements as it is revolved therein around the axis of adjusting shaft 149.

The fluid ports 167 of the bank of valves B communicate with a common manifold chamber 168 which is formed by an annular recess in the face of end plate 162, and similarly fluid ports 167 of the bank of valves A communicate with a common manifold chamber 169 in the opposite end plate 162. Manifold chamber 168 is provided with a fluid fitting 1711 to which fluid conduit members are attached; and chamber 169 is provided with a similar fluid fitting 171. I

in the operation of the selector valve mechanism one ofthe manifold chambers is supplied with high pressure fluid and the other is connected with the low pressure discharge line. The high pressure fluid is supplied from the high pressure manifold chamber through one of the valves communicating therewith and through fluid circuit conduits to the cylinder devices connected to such valve. Fluid discharged from the energized cylinder device is returned through fluid lines to the corresponding valve unit in communication with the low pressure manifold, thus completing the fluid actuating circuit. The two corresponding valves in each of the valve banks are actuated in unison by the cam element 174, such as in Fig. 18, wherein the valves actuating elements of valves A and B are simultaneously engaged by the cam element. As the shaft 149 is rotated through its operative positions in the manner hereinbefore described, the cam element comes into engagement with the valve elements of successive corresponding valve units in each of the banks A and B opening the fluid circuit associated with each set of valves. Intermediate valve bank C comprises a series of circumferentially-located valve units which are actuated simultaneously with corresponding valves in banks A and B to completefluid circuits including the valves C in addition to the corresponding units in banks A and B wherein compound movement of the table is effected, as will be described hereinafter. The conduits received on the fluid fittings and 171 are connected'with the reversing valve 147 whereby the high and low pressure lines may be alternatively connected with either of the manifold chambers 168 and 169 to control the direction of fluid movement in the circuits and therefore the direction of movement of the cylinder devices.

. Each of the operative positions of the shaft 149 is indicated by the pointer 145 which registers with the corresponding marking on the dial face 144. The markings on the dial face are identified in Fig. 17 by references from a to j which designate the table movement performed by the hydraulic circuit for that setting. The respective table movements corresponding to each of the references are as follows: a-table height; bleg section; ckidney bridge; d-center break; e-reflex abdominal; fside tilt; g-Trendelenburg; hTrendelenburg with leg; ichair position; jchair without leg. The major positions of the table are shown in Figs. 28 through 31 wherein Fig. 28 illustrates a Trendelenburg position; Fig. 29 illustrates a center-break position; Fig. 30 illustrates a reflex abdominal position; and Fig. 31 illustrates a chair position.

The shaft 149 and cam adjusting mechanism for the selector valve are centered in the respective operating positions by a detent mechanism 176 which is shown in the Fig. 16 and also in Figs. 14 and 18. In this mechanism a collar 177 is fixed on the shaft 149 on' which is secured a sprocket plate 178. The sprocket plate is irregular in contour having a series of depressions, or notches, 179, numbering ten in all, that correspond to each of the operative positions of the adjusting shaft 149. Pins 180 comprising roller elements are provided to engage the sprocket plate at diametrically opposite points. These pins are carried in link members 181, each of which is pivoted at one end on posts 182 set in the selector valve housing and having free outer ends. Springs 183 are hooked on pins 184 on the free ends of link members 181 and are anchored on one of the adjacent fixed posts 182. As seen in Figs. 14 and 18, the link members 181 comprise spaced parallel plates between which the pins 181 are mounted. Thus the pins 180 are resiliently biased toward the sprocket plate in such a manner as to engage in the depressions 179'Wl'll6h are oriented with respect to the operative positionsof the shaft 149 and therefore center the shaft and cam actuating mechanism in each position. At the same time the links are adapted to expand when sufficient torque is appliedto the selector valve adjusting shaft, as 'indi cated by the dotted line positions, so that the pins may ride over the sprocket plate between the successive .depressions. As a result of this construction, substantially no resultant lateral forces are exerted on the adjusting 13 shaft 149 by the detent mechanism. Thus frictional hearing forces are reduced to a minimum and the adjustment of the valve mechanism is facilitated.

The reversing valve 147 embodies a pair of valves L arranged circumferentially in one plane and pairs of valves R and R which are arranged in separate circumferential banks. Each of these valve units is substantially identical to the valve units inserted in the cylinder valve housing 146. As shown in Fig. 18, the valve element in each of the valve units protrudes into a central cylindrical bore 185 wherein the end of shaft 148, having a bushing 186 thereon, is received. The bushing 186 is provided with flat depressions 187 and 188, each of which has a diametrically opposite counterpart not visible in Fig. 18, and a flat 189. The oppositely disposed flats 187 are shown in the sectional view of Fig. 23. In the normal position of the shaft 148 the depressions 187 and 188 register with the protruding ends of the corresponding valve actuating elements which are accommodated therein, allowing all of the valves to remain closed. When the shaft 148 is rotated in the cylindrical bore, the engaging portions of the bushing 186 depress the valve actuating elements and open the valves. The valve elements in valve units R are disposed ofl-center with respect to the notched face 187 (as illustrated in Fig. 23, and as more fully disclosed in said co-pending application of E. F. Fullwood, Air Reduction Patent Project No. 216), both of these elements protruding through the upper wall of the cylindrical chamber 185. The valve elements of the valves R are similarly disposed with respect to the flat faces 188. In this manner. when the shaft 148 is rotated in a clock-wise direction, one each of the valves R andR' are opened while the other valves in each pair remain closed, and when the shaft is rotated in a counterclock-wise direction, the other valves are opened. In addition, the flat 189 by design constitutes a smaller peripheral depression than the flattened portions 187 and 188, and the valve element of the valve L is centrally positioned with respect thereto. As a result the valve L is actuated during the initial rotation of shaft 148 in either direction prior to the actuation of the valves R and R.

The shaft 148 is biased toward its neutral position (all valves closed) by a centering mechanism 190. This mechanism includes a collar 191 mounted on the protruding end of shaft 148 and having a radial flange 192. A lug 193 projects inwardly from the flange and is adapted tobe received in the split end of pin 194, set into the housing 147. A coil spring 195 is carried loosely on the collar 191, Fig. 15, and is provided with sharply-bent ends 196 which are crossed and sprung so as to pinch inwardly around the pin 194. Thus the spring ends 196 urge the lug 193 and pin 194 into mutually intersecting positions, such as shown in Fig. 15, which correspond to the neutral position of the shaft 148.

In the operation of the reversingvalve, the high and low pressure fluid lines of the table circuit deliver fluid thereto through conduits hereinafter described in connection with the circuit diagram of Fig. 20. When the shaft 148 is rotated by manipulation of lever 161, seen in Fig. l, valve L is opened to admit fluid to the reversing valve units R and R. The eifect of rotating the shaft 148 in either a clock-wise or a counterclock-wise direction from the neutral or closed position is to complete the fluid connections between the high and low pressure conduits and the manifold chambers of the selector valve in either of two reverse directions, thus determining the direction in which the actuating fluid is supplied to the manifolding chambers in the cylinder valve housing. When the shaft 148 is in its neutral position the line valve L is closed, no fluid is circulated in the control circuit, and the table mechanism is immobile.

It will be seen that by selective adjustment of the hand knob 154 the desired operation of the operating table mechanism may be selected and then by adjustment of lever 161 the actuating fluid may be circulated through 14 the system to cause such operation in the desired direction.

The table control circuit comprises two distinct portions or systems; the distribution system (Fig. 20) which includes the selector valve assembly, the several fluid cylinder devices, and fluid lines connecting with each cylinder device, and the supply system (Fig. 21) which includes the reversing valve assembly, the reservoir, pump, pressure responsive switch, pressure limiting means, and the several fluid fittings and conduits. The elements of the control circuit are so arranged that only two connecting conduits are necessary to link the portion of the circuit in the table base with the portion of the circuit in the pedestal-mounted frame structure. Thus, the high and low pressure sides of the fluid pump are connected with conduits which extend through the table pedestal, and in turn connect with the master valve unit. The two conduits passing through the pedestal comprise the two telescoping tubular conduits 200 and 201, seen in Figs. 1, 3, l2, and 13. Conduit 200 corresponds to the high pressure fluid for delivering fluid to the reversing valve assembly in the master valve assembly, and conduit 201 corresponds to the low pressure fluid which returns fluid from v the reversing valve assembly to the storage reservoir. The conduits have fluid-tight slide fittings 202, Fig. 13, which permit the lengths of the conduits to be varied in accordance with the adjusted height of the operating table.

The table base 10 houses several of the elements of the supply portion of the circuit. Referring first to the sectional views of the table base in Figs. 12 and 13, the arrangement of this portion of the circuit may be seen. The pump 23, mounted on the motor 22 at one side of the reservoir container 20, is connected by a conduit 203 to the reservoir through a T-fitting 203'. A series of connected lengths of tubing 204, which also include a pair of check valves 205 and 206 etXend from the outlet of the pump to the lower end of the telescoping conduit 200, within the table pedestal, through which high pressure fluid is administered to the reversing valves and thence to the distributing portion of the hydraulic circuit. The low pressure telescoping conduit 201, through which low pressure fluid is returned from the distributing portion of the circuit, connects at its lower end with tubing 207 which enters through the side of the reservoir container at 208.

The electric motor 22 is connected to a source of power by power cord 22' which attaches to the motor through a pressure-responsive switch 209. The switch is provided with a tap line 210 which is received in a T-fltting 210' in the high pressure line 204- whereby the switch is closed and opened in response to variations in the fluid delivery line pressure below and above selected pressure As will later be illustrated, the line pressure is affected by manipulation of the master valve mechanism when it is adjusted for operation of the table mechanism which automatically results in actuation of pressure switch 209 which controls the motor 22. Fluid is thus automatically pumped through the table control circuit when the master valve controls are adjusted and opened for table operation, without requiring other control adjustment for the motor. Similarly, when the circircuit connections are closed, increase in fluid pressure in the delivery line above a selected upper limit causes the switch to open the electric circuit to the motor and stop the pump. The switch 209 also prevents overloading of the fluid circuit by excessive pressure.

An accumulator device 211 is connected with the high pressure line 204 through a branch tube 211'. This device is a standard apparatus which is adapted to maintain the desired line pressure when the pump is not in operation by compensating for leakages which may occur in the circuit. The device is conventionally provided with a spring-loaded plunger acting on a small volume of fluid contained therein which is connected through the tube 211' and a one-way restrictor valve 211" with the high pressure supply line. Thus, should fluid leakages occur in the circuit, the loss in volume is. accommodated by retraction of the plunger which is compressed by spring loading to maintain the fluid in" the circuit at the necessary pressure. 22 from cycling when the circuit is not in operation. When the reserve volume of fluid in the accumulator is depleted, as'by more than ordinary leakage, or when the table has not been operated for a long period, pressure switch 209 closes, causing momentary operation of the pump 23 which restores the required line pressure and recharges the accumulator. The valve 211" prevents sudden introduction of fluid at a high rate of flow into the control circuit which would produce a surge, or lurch, in the table operation.

An alternate source of high pressure fluid for the control circuit is, provided for emergency use, such as in the event of a power failure. Such alternate source comprises the foot pump 14 which is provided with an inlet tubing 212 connecting with the reservoir fitting 203 and an outlet tube 212 which is connected with a two-way valve device 213. In the normal position of the valve, as indicated by the handle 213', fluid pumped through the foot pump is administered to the caster cylinders 13, asbefore described. When the valve handle is in its second operating position, fluid is delivered from the valve through a conduit 214 which is received on the cross fitting 204' in the high pressure supply line 204. Thus, in an emergency the foot pump may take the place of the motor-driven pump 23 in supplying high pressure fluid to the control circuit for actuation of the table.

Thecontrol circuit for the table is preferably adapted to utilize a non-compressible, or hydraulic, actuating fluid; such, for example, as a conventional hydraulic cylinder oil. are provided in accordance with standard practices and constitute standard parts commonly used for such purposes. Elements of the control circuit are shown schematically in the circuit diagram. Several ofthe schematic symbols are taken from the standard symbols given by the Joint Industrial Conference (I. I. C.) on Hydraulic Standards for Industrial Equipment, and several reference numerals'applied to parts of the table hereinbefore are applied'to the same elements schematically shown in the circuit diagrams.

In order to clarify the control circuit diagram as much as possible, it has been divided into two separate but related figures. Fig. 20' illustrates the distributing portion of the circuit, and Fig. 21 illustrates the supply portion of the circuit, these portions of the. circuit being connected through the manifold chamber conduits at the right side of Fig. 20 and left side of Fig. 21. In the supply part of the circuit iniFig; 21 it will be seen that fluidis delivered from thereservoir through the pump inlet line 293, pump 23, and the high pressure line 204 to a conduit 290' which is connected to the line. valve L of the reversing valve housing 140. The line 299 in the circuit diagram schematically represents all of the seriesconnected conduits extending from the pump outlet conduit 204 in the table base, Fig. 12, and connecting with line valve unit L of themaster valve, including the telescoping conduit 296 which extends through the pedestal.

The alternative system for supplying high pressure fluid in the control circuit is seento include the fluid line 212 which supplies fluid from the reservoir to the foot pump 14, pump outlet line'212', and connecting line 214 which delivers the high pressure fluid from the two-way valve 213 to the line. 204 at junction 204. When the twoway valve 213 isset for delivering fluid from the foot pump to the caster cylinders, as illustrated by the position' of the valve'adjus'ting handle 213 in the circuit diagram, the line 214 is closed. The fluid introduced into the caster cylinders maybe bled back into the reservoir by operating the valve handle 17 which manually opens the check valve units '17 in the foot pump. 7

This device thereby prevents the motor In the circuit the various hoses, tubes, and fittings The emergency supply line. 214 is tapped into the high pressure line between the check valves 205 and 206. Valve 205 thus prevents reverse flow of the fluid delivered by the foot pump 14 into pump 23 when the emergency supply source is used. The emergency supply line 214 is provided with. a venting valve 214' through which fluid pressure may be relieved in the system'in the event that the foot pump is inadvertently operated beyond the prescribed pressure capacity of the circuit. This valve also functions when the motor pump 23 is in operation as a safety device in the event that the pressure switch 209 fails to shut 0d the motor 22 at the prescribed line pressure. Fluid vented through the valve is returned to conduit 207 and thence to the reservoir.

When the fluid admitted to the selector valve has been circulated in the distribution portion of the control circuit, hereinafter described in connection with Fig. 20, and is returned to the reversing valve assembly, it is delivered into a common conduit shown at 201' connecting with the reversing valve, inthe circuit diagram of Fig. 21. in the diagram this conduit line schematically represents the series-connected fluid conduits connecting the reversing valve with the return discharge line 207 and the fluid reservoir in the table base, Fig. 12, including the return telescoping conduit 201 which extends through the table pedestal. A variable pressure relief valve 215. is placed in'the discharge line, 201' through which the low pressurefluid is discharged. The valve 215 is triggered by the high pressure fluid through a tap line 215' connecting with the high pressure fluid in conduit 216 whereby the low pressure fluid discharge is regulated to prevent excessive cylinder displacement speeds. The valve is preferably mounted in the table frame. so that the tap line 2155 may connect-with the high pressure line at the master valve unit, also mounted in the frame, thus eliminating any necessity of an additional expandable conduit passing through the pedestal from the table base. In the circuit the discharge of the hydraulic fluid from the cylinder devices is, under certain conditions, restrictedlby the variable pressure relief valve to prevent the cylinders from moving at excessive rates of speed. Inasmuchas double-acting cylinders are employed in the circuit and the loads applied thereto are reversible on some of the cylinders, the relief valve means is provided to limit the rate of discharge of oil from the cylinders when the cylinders are moved in the direction of the load. An example. is in the operation of the pedestal cylinder wherein it will be seen that hydraulic fluid in raising, the table and supporting the load thereon is pumped into the cylinder above the piston while the fluid below the piston may be discharged at atmospheric pressurev without difliculty. In the reverse condition Whenit is desired to pump fluid into the lower portion of the cylinder to lower the table, the discharge ofoil above the piston must be restricted to provide a gradual, uniform descent of. the table and avoid pulling a vacuum.

against the marginal spring seating force to reduce the restriction of the discharge fluid withoutimposing unnecessary load on the pump motor. ditien-(when the cylinder is moving in the direction of the load force) the pressure applied to the reliefvalve is smalhenabling the spring force to close' the valve and thus. throttle or restrict the discharge flow of cylinder fluid. and prevent excessive cylinder-piston displacement speeds Thus in the case of lifting a load this fluid pressure isv suflicient to open the relief valvecompletely' In the reverse con' 

